A dot connector circuit is a circuit used to interconnect discrete points during the reconstruction of an analog waveform from digitally stored data. Such a circuit is necessary whenever digitally stored data are to be displayed, for example, on an oscilloscope. An analog waveform must be generated from the data to be used to drive the amplitude input, or Y-axis, of the oscilloscope. It is highly desirable that data points along the waveform be connected with straight lines of uniform intensity for this purpose.
In the prior art, dot connector circuits have been based on several different approaches. One of the most straight forward of these is to employ a digital-to-analog converter to drive the Y-axis of an oscilloscope directly. In this approach, staircase waveforms approximate diagonal lines. The accuracy of this approximation therefore depends upon the resolution of the digital-to-analog converter used; thus, the lower the resolution is, the coarser or larger the staircase steps will be. In practice with this approach then, there is the disadvantage of requiring a very high resolution converter in order to accurately and smoothly reconstruct the analog waveform.
A second method which has been used is to follow the digital-to-analog converter of the preceding method with a resistive-capacitive (RC) low pass filter. Inclusion of the low pass filter has the effect of smoothing the sharp edges of the staircase waveform. This approach, however, has the disadvantage of resulting in displays in which the data points are connected with exponential curves rather than straight lines.
Another approach in the prior art dot connector circuits uses two digital-to-analog converters. These converters are time-multiplexed; further, a triangle waveform is required to serve as the reference voltage inputs for these converters. Data points are fed alternately to one converter and then to the other. The outputs of the two converters are then summed, and the result of this summation is a waveform which forms a ramp from each data point to the next. Since the linearity of the ramps connecting data points depends on the piecewise linearity of the triangle waveform, this method then exhibits the disadvantage of requiring a perfect triangle waveform for good linearity. Furthermore, this method requires two converters rather than one as in some other methods.
Still another method of waveform regeneration is to follow a digital-to-analog converter with a summing amplifier. A second input to the summing amplifier is fed back from the overall output of the circuit. The output of this amplifier is a voltage proportional to the difference between the last data point and the next data point level. This difference is fed to a sample-and-hold amplifier, and then applied for a fixed time to the input of a standard integrator. The output of this integrator is buffered and then used to drive an oscilloscope. The result is a series of straight lines connecting the data points, but at the expense of a large number of parts and a very complex circuit. Timing of control signals for this approach is also a disadvantage: the timing is very critical.